Chemical vapor phase epitaxial device

ABSTRACT

A chemical vapor deposition apparatus is provided. The chemical vapor deposition apparatus includes a susceptor support base and a susceptor, and configured to rotate the susceptor with a rotary shaft, a gap as wide as about 1 mm or more is provided along the boundary between the support base and the perimeter of the susceptor to prevent Ga from forming bridges between the support base and the susceptor during growth of III-V compound semiconductors such as GaN, thereby preventing disturbance of rotation.

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] The present application claims priority to Japanese PatentDocument No. P2001-246177 filed on Aug. 14, 2001, the disclosure ofwhich is herein incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] This invention relates to a chemical vapor deposition apparatus,especially suitable for application to a metal organic chemical vapordeposition (MOCVD) apparatus.

[0003] Devices manufactured by using III-V compound semiconductors, suchas light emitting devices including LEDs and semiconductor lasers, andother devices like communication-purpose high-frequency transistors, areimportant devices constituting hardware infrastructures of the moderncommunication society, together with silicon (Si)-based devices.

[0004] III-V compound semiconductor devices, having structuresingeniously making use of hetero junctions of III-V compoundsemiconductors, take a complementary part with Si-based devices inregions impossible to realize with Si.

[0005] For manufacturing compound semiconductor devices including III-Vcompound semiconductors, excluding simple-structured devices such asMESFET, hetero epitaxial techniques are important techniques. It is noexaggeration to say that hetero epitaxial techniques basically supportthe manufacture of such devices. Molecular beam epitaxy and chemicalvapor deposition, in particular MOCVD, are currently major heteroepitaxial techniques, which have been studied in laboratories since1960s.

[0006] MOCVD was bought into practice as an epitaxial growth techniquefor manufacturing GaAs semiconductor lasers. Currently, an MOCVDapparatus enabling epitaxial growth on a number of substratessimultaneously is commercially available. In terms of componentialtechniques of the multi-substrate MOCVD apparatus, there are varioustypes. Regarding the susceptor configuration, there are a barrel typeand a pancake type. In terms of the gas flow mode, there are ahigh-flow-rate horizontal type, high-revolution type, vertical down-flowtype, and so on. In terms of the substrate-supporting mode, there areschemes of putting substrates above the gas flow (face-down) or puttingsubstrates under the gas flow (face-up). Regarding heating there are aRF induction heating type, electrical resistance heating type, lampheating type, and so on. These componential techniques are combinedvariously to make up various types of MOCVD apparatuses.

[0007] Conventional MOCVD apparatuses for epitaxial growth of III-Vcompound semiconductors uses gallium (Ga), aluminum (Al) or indium (In)as a group III element and arsenic (As) or phosphorus (P) as a group Velement, and the growth temperature was 800° C. at most. On the otherhand, there is a recent demand for an MOCVD apparatus capable ofepitaxially growing GaN compound semiconductors using ammonia (NH₃) as asource material.

[0008] A MOCVD apparatus for GaN semiconductors is configured to invitereaction of a group III organic metal compound and ammonia (NH₃) at atemperature around 1100° C. to grow a single-crystal thin film on asapphire or SiC substrate. Concerning the single-crystal thin film, gascomposition and growth conditions for growing high quality crystals wereacademically reported and known. However, MOCVD apparatuses forrealizing optimized gas composition and growth conditions for obtaininghigh quality crystals have been modified after individual technicalresearches, and almost none of their actual improvements are known.Among some known MOCVD apparatuses, there are some proposals directed tothe structure of the reaction tube (for example, Japanese PatentLaid-open Publications Nos. JP-H02-288665A, JP-H04-94719 A andJP-H11-12085). Even with these techniques, it has been difficult tomanufacture semiconductors of long-lasting good crystal qualities underacceptable reproducibility because of various entangled factors.

SUMMARY OF THE INVENTION

[0009] The present invention generally relates to a chemical vapordeposition apparatus, particularly a metal organic chemical vapordeposition (MOCVD). The present invention provides a chemical vapordeposition apparatus optimized for obtaining quality high crystals byepitaxial growth of compound semiconductors, and especially GaN compoundsemiconductors.

[0010] The Inventor continued vigorous studies to overcome theabove-discussed problems involved in the prior art techniques. Thecontents of the studies are introduced hereunder.

[0011] A chemical vapor deposition apparatus typically includes asusceptor, and a support base holding the susceptor, as shown in FIG. 1.The susceptor is designed to rotate on its own axis relative to thesupport base. In FIG. 1, reference numeral 1 denotes the support base, 2is the susceptor, 3 is a substrate, 5 is a rotation axis for rotation ofthe susceptor, and 6 is a heater. The heater 6 is put in the supportbase 1 in some designs. The support base 1 may be configured to rotatein some designs. Rotation of the susceptor 2 enhances the uniformity ofthickness of the film deposited on the substrate 3.

[0012] After repeated use of the apparatus, decomposition productsaccumulate as sediments 4 on the susceptor 2 and the support base 1, andsediments 4 accumulating along the boundary between the support base 1and the susceptor 2 under relative movements disturbs the rotationalmovements. It has been recognized that a serious problem occursespecially when growing gallium nitride semiconductors. For growth of agallium nitride semiconductor, the substrate surface is cleaned with aflow of hydrogen for 10 minutes at 1100° C., for example. In this hotcleaning process, nitrides accumulated on the susceptor 2 in thepreceding manufacturing process decompose, and metallic gallium remainsin form of small droplets on the surface. Liquid gallium near theboundary between the susceptor 2 and the support base 1 makes smallballs by surface tension, and invites bridging at the boundary betweenthe susceptor 2 and the support base 1. When ammonia gas is supplied forthe next growth step, liquid metallic gallium nitridized, and solid ofgallium nitride again grows along the boundary as shown by numeral 41.The GaN solid having intruded into the boundary seriously disturbsrotation of the susceptor 2, and may ultimately cause mechanicaldestruction. Therefore, it will be effective to separate the susceptor 2and the support base 1 by a distance wide enough to prevent formation ofbridges by metallic gallium.

[0013] The support base including the susceptor may be configured toincline from the upstream to the downstream of the gas flow to increasethe flow rate of the gas. This will contributes to uniforming the filmin thickness. In vapor deposition of nitrides, however, accumulatednitrides may cause the above-explained undesirable problem following theprocess of changing to liquid metallic gallium, moving along theinclined surface into the gap between the susceptor and the supportbase, making bridges of metallic gallium therebetween, and forming thesolid in the next step supplying ammonia. Therefore, to prevent thisphenomenon, it will be effective to make grooves of ridges and furrowson the support base and thereby block the flow of metallic galliumdroplets beyond the grooves.

[0014] Known techniques use the mechanism as show in FIG. 2 to rotatethe susceptor 2, in which the support base 1 and susceptors 21 haveformed annular grooves equal in diameter and hold carbon balls 91 in thegrooves. Gears 93 are formed at end portions of the susceptors 21 anddriven by external stationary gears 8 to realize rotational movementsreduced in friction. However, since the susceptors 21 and the supportbase 1 are not integral, the susceptors 21 may jump and disengage undervibrations when the rotation speed increases. Especially in a growthapparatus for growth of nitride compound semiconductors at hightemperatures, in which SiC-based materials having rough surfaces areoften used, improvement of the susceptor structure has been longed for.Therefore, it will be effective to provide an independent bearingmechanism between each susceptor 21 and the support base 1.

[0015] There is a type of mechanism for rotating the susceptor, whichcannot rotate the center axis of the susceptor directly. A typical wayfor coping with it uses a gear on the circumference of the susceptor todrive the gear with an external gear. In this case, however, if thetemperature is raised high for growth like the growth apparatus ofnitride semiconductors, it is necessary to cope with the problem ofrelative positional offset by thermal expansion and the problem of anincrease of the frictional force. Therefore, if new system is employed,which includes a mechanism located on the circumference of one ring ofsusceptors or bearings to resist against wind pressure and an inlet tubeintroducing a gas flow into the mechanism, it is possible to preventirregular torque by slipping. Thus, the new system is effective againstdestruction of rotating members by relative positional offset andagainst an increase of the frictional force.

[0016] As a way of heating the susceptor, there is a lamp-heated systemthat have actually been employed in a nitride compound semiconductorgrowth apparatus of a normal pressure type (Japanese Patent Laid-openPublication No. JP-H11-12085A). Among apparatuses of a reduced pressuretype, there are only a few examples using a heating lamp. Especiallyamong growth apparatuses for nitride compound semiconductors, noapparatuses have heretofore employed lamp-heated systems. However, thisis made possible by employing a system in which the lamp house itselfforms a part of the depressurizing container.

[0017] With regard to a mechanism for rotating a large-scaled rotationalsusceptor or support base, some apparatuses employ a system not holdingthe center axis of rotation. For example, as shown in FIG. 3, in case adonut-shaped carbon susceptor 2 is located to encircle the support base1 made of a rotatable quartz disk having a center axis, and thedonut-type carbon susceptor 2 alone is heated, it is impossible tointegrally fix the support base 1 and the susceptor 2 because thesupport base 1 made of quarts and the susceptor 2 made of carbon aredifferent in thermal expansion coefficient. Therefore, their relativepositions vary with temperature. In another configuration as shown inFIG. 4, in which a plurality of susceptors 21 attached on a largerotatable support base 1 having a center axis of rotation is rotatedboth about its own axis and together with the support base 1 by astationary gear 8 located to encircle the them together, the stationarygear 8 around them must be isotropically expanded (contracted) inresponse to the thermal expansion (contraction) of the rotationalsupport base 1 while maintaining it center stationary when thetemperature rises (or decreases). If not, gears will fail to biteproperly and will break ultimately. Reaction apparatuses such as growthapparatuses for nitride compound semiconductors, which are required towork at growth temperatures as high as 1100° C., are subjected to largethermal expansion. Therefore, unless the outer-circumferentialstationary gear 8 is expanded while keeping its center axis stationary,the outer-circumferential stationary gear 8 cannot engage accuratelywith the gears 90 of the susceptors 21 attached on the rotatable disk,and will become unable to drive the susceptors 21. Therefore, it isindispensable to use a structure for maintaining the center point at aconstant position upon isotropic deformation like thermal expansion of amember whose center cannot be fixed physically. As a structure for thispurpose, it is useful to provide connection rods at some positions onthe member having rotation symmetry to extend equally in length andequally in angle from diametric lines passing their positions, and toconnect the opposite ends of the connection rods to a member independentfrom the member having rotation symmetry. Thus, the center point of themember is maintained constant even upon isotropic deformation thereof.

[0018] For immediately stopping a drive mechanism (motor) in therotating system for driving the center axis directly upon anyextraordinary friction on the part of the rotating member, a slipmechanism was typically used heretofore between the drive mechanism andthe rotation axis. This system certainly stops the rotating member byslipping. However, it is impossible to know the occurrence of theextraordinary phenomenon at that moment. Taking it into account, it iseffective to develop this mechanism by introducing a rotary encoderbetween the rotational member and a slipping member or a torsionallydeformable member to know any irregularity by processing the rotationoutput of the rotary encoder and the rotation output from the drivemechanism with a comparator and an information processing device, so asto stop the drive mechanism and generate an alarm signal.

[0019] As an alternative of the mechanism for stopping the drivemechanism, it is also effective to equip the drive mechanism itself, andan air-driven type mechanism will be effective for this purpose.

[0020] For MOCVD of III-V compound semiconductors, a plurality of sourcematerial gases are used. It has been acknowledged that confluence pipesmust be properly arranged to bring source material gases controlled inflow rate into confluence with the main tube communicating with thereactor. For example, if two pipes merge to collide head-on with eachother as shown in FIG. 5, then the gases from two pipes collide andinterfere each other, vibrations produced thereby makes it impossible toproperty control the flow rate. Therefore, for bringing a plurality ofpipes containing source material gases into confluence, it has beenconfirmed effective to employ a structure in which the pipes do notconfront head-on, or the pipes merge at points offset by at least adistance corresponding to the diameter of the pipe.

[0021] The present invention has been made based upon theabove-explained researches by the Inventor.

[0022] In an embodiment, the first aspect of the invention is a chemicalvapor deposition apparatus that includes a gap that is provided alongthe boundary between a support base and the perimeter of a rotationalsusceptor supported on the support base.

[0023] To reliably prevent the bridging, the width of the gap along theboundary between the support base and the perimeter of the rotatablesusceptor is preferably determined to be equal to or wider than about0.5 mm, or more preferably determined to be equal to or wider than about1 mm. On the other hand, if the gap is excessively wide, material gaseswill readily intrude in the gap and will accumulate on its sidewalls.Therefore, to prevent it, the width of the gap is preferably determinednot to exceed about 3 mm, or more preferably determined not to exceedabout 2 mm. Similarly, depth of the gap is preferably determined to beequal to or deeper than about 1 mm, or more preferably determined to beequal to or deeper than about 2 mm. On the other hand, depth of the gapis preferably determined to be shallower than or equal to about 4 mm, ormore preferably determined to be shallower than or equal to about 3 mm.

[0024] The second aspect of the invention in an embodiment is a chemicalvapor deposition apparatus including a support base, and a rotationalsusceptor attached to the support base with an inclination relative tothe direction of gravity, wherein grooves of ridges and furrows areformed on the support base so that a decomposition product of a gas isaccumulated in the grooves.

[0025] The third aspect of the invention in an embodiment is a chemicalvapor deposition including; a support base; and a susceptor rotatingmechanism including a bearing mechanism fixed to the support base andhaving a rotation transmission gear, and a susceptor fixed to one ofrotating rotational members of the bearing to rotate therewith.

[0026] To incorporate a pair of opposed rotational members via balls,the bearing mechanism typically has a bearing structure in which thepair of rotational members are concentrically threaded so that, onceboth members are joined and relatively rotated beyond the threadingengagement, the ridges of the threads function as disturbances againstdisengagement of the members and hold them integrally.

[0027] The fourth aspect of the invention in an embodiment is a chemicalvapor deposition apparatus including a support base; and a susceptorrotating mechanism having a bearing mechanism fixed to the support baseand a susceptor fixed to one of rotational members of the bearing torotate therewith, wherein one of the opposed rotational members includesa mechanical portion for receiving wind pressure, and a mechanism forguiding a gas flow to the mechanical portion.

[0028] The fifth aspect of the invention in an embodiment is a chemicalvapor deposition apparatus having an external heating means and areaction chamber that are separate chambers separated by a partitionplate, wherein a communication passage is provided near a gas dischargeoutlet to equalize the external heating means and the reaction chamberin pressure.

[0029] The sixth aspect of the invention in an embodiment is a chemicalvapor deposition apparatus including a structural body having a rotationsymmetry and not fixed in position of its center point; and a structurefor keeping the position of the center point against isotropicdeformation such as thermal expansion of the structural body.

[0030] To keep the position of the center point, a plurality ofconnection rods are provided to extend from a plurality of points on themember having the rotation symmetry in directions equally offset fromthe diametric directions, and connected to a member independent from themember having the rotation symmetry at equally distant positions fromthe member having the rotation symmetry.

[0031] The seventh aspect of the invention in an embodiment is achemical vapor deposition apparatus including a rotary encoder as amechanism for detaching a drive force upon extraordinary torque causedby a failure of a substrate rotting mechanism; a slip or deformableconnector to cope with extraordinary torque, and a mechanism forstopping a driver depending upon a result of comparison between therotation signal of the rotary encoder and the rotation signal of thedriver.

[0032] The eighth aspect of the invention in an embodiment is a chemicalvapor deposition including an air driver directly connected to a rotaryshaft as a mechanism for detaching a drive force upon extraordinarytorque caused by a failure of a substrate rotating mechanism so that theair driver slips upon generation of extraordinary torque.

[0033] The ninth aspect of the invention in an embodiment is a chemicalvapor deposition includes that a plurality of pipes containing sourcematerial gases merge a unit pipe structure at positions preventinghead-on collision of the pipes, or at positions distant by at least thediameter of the pipe.

[0034] The invention is suitable for application to metal organicchemical vapor deposition apparatus among various types of chemicalvapor deposition apparatuses. Especially, it is suitable for use ingrowth of III-V nitride semiconductors containing a group III elementsuch as gallium (Ga), aluminum (Al), boron (B) and indium (In), and agroup V element, such as of nitrogen (N), phosphorus (P) and arsenic(As), and the like.

[0035] Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the figures.

BRIEF DESCRIPTION OF THE FIGURES

[0036]FIG. 1 is a cross-sectional view showing the substantial part of aconventional chemical vapor deposition apparatus.

[0037]FIG. 2 is a cross-sectional view showing the substantial part ofanother conventional chemical vapor deposition apparatus.

[0038]FIG. 3 is a plan view showing a particular part of still anotherconventional chemical vapor deposition apparatus and a correspondingpart of a chemical vapor deposition apparatus according to an embodimentof the present invention.

[0039]FIG. 4 is a plan view showing a particular part of yet anotherconventional chemical vapor deposition apparatus and a correspondingpart of a chemical vapor deposition apparatus according to an embodimentof the present invention.

[0040]FIG. 5 is a schematic diagram showing a pipe system of aconventional chemical vapor deposition apparatus.

[0041]FIG. 6 is a cross-sectional view showing the substantial part of achemical vapor deposition apparatus according to an embodiment of thepresent invention.

[0042]FIG. 7 is a cross-sectional view showing the substantial part of achemical vapor deposition apparatus according to an embodiment of thepresent invention.

[0043]FIG. 8 is a cross-sectional view showing the substantial part of achemical vapor deposition apparatus according to an embodiment of thepresent invention.

[0044]FIG. 9 is a cross-sectional view showing the substantial part of achemical vapor deposition apparatus according to an embodiment of thepresent invention.

[0045]FIG. 10 is a cross-sectional view showing the substantial part ofa chemical vapor deposition apparatus according to an embodiment of thepresent invention.

[0046]FIG. 11 is a schematic diagram showing the substantial part of achemical vapor deposition apparatus according to an embodiment of thepresent invention.

[0047]FIG. 12 is a pipe system in a chemical vapor deposition apparatusaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0048] The present invention generally relates to a chemical vapordeposition apparatus, particularly suitable for a metal organic chemicalvapor deposition. Some embodiments of the invention will now beexplained below in detail with reference to the drawings.

[0049]FIG. 6 shows configuration of a reactor in a chemical vapordeposition apparatus according to the first embodiment of the invention.In FIG. 6, reference numeral 1 denotes a support base made of a quartsmaterial. Numeral 2 denotes a SiC-coated susceptor, and numeral 3denotes a sapphire substrate. Numeral 5 denotes a rotary shaft forrotating the susceptor 2, 6 is a heater, and 7 is a reactor made ofstainless steel. The process for crystal growth of GaN is explainedbelow. First introduced is hydrogen gas into the reactor 7. Then, thereactor 7 is heated to about 1100° C. for about 15 minutes to clean thesurface of the sapphire substrate. Then, the temperature is lowered toabout 550° C., and ammonia and trimethyl gallium (TMG) is supplied todeposit amorphous GaN up to a thickness around 30 nm. Thereafter, thesupply of TMG is interrupted, and while ammonia and hydrogen aresupplied, the temperature is raised to about 1100° C. to crystallize GaNaccumulated under a low temperature. Subsequently, TMG is again suppliedto accumulate single crystal GaN on the micro seed crystals. The processof these sequential steps is known.

[0050] After completion of the crystal growth, the substrate is removed,and a new sapphire substrate is set on the same position for the nextgrowth round. The condition at the start of the second growth round isdifferent from that of the initial growth round in that GaN existsaround the susceptor 2 or on the support base 1. This GaN sedimentdecomposes in hydrogen in the process of cleaning the substrate surfaceas the first step of the second growth round because of a hightemperature, and makes micro metal droplets of Ga. The sediment is shownat 4 in FIG. 1. FIG. 1 shows configuration of the susceptor and itsperipheral members in a conventional chemical vapor depositionapparatus. The rotational susceptor 2 and the support base 1 aretypically formed not to interpose a gap within the extent of the currentmachining accuracy. Actually, however, there inevitably exists the gapof approximately 0.1 mm. Metallic gallium produced may exist above thegap, i.e. along the boundary between the susceptor 2 and the supportbase 1, and it appeared to intrude into the gap experientially. Althoughits mechanism is not clear, it will be possible to suppose that microdroplets join and become a certain size, and intrude into the gap bysurface tension. This is shown at 41 in FIG. 4.

[0051] In the next process of supplying ammonia to form gallium nitride,the Ga metal is nitridized by ammonia, and again forms GaN.Responsively, simultaneously with the solidification, it expands involume and produces a strong frictional force that disturbs rotation.Ultimately, it may lead to destruction of the mechanisms. In view ofsuch experiential phenomenon, the first embodiment of the invention addsan improvement as shown in FIG. 6. That is, against the common knowledgeof sizing them not to produce a substantial space between them, theembodiment makes a space around 1 mm or more between them, and the gapis dug down to a depth equal to or deeper than 2 mm. This is shown at 11in FIG. 6. In this configuration, even when the GaN accumulated on thesupport base 1 changes to Ga metal, it does not form bridges to thesusceptor 2, and therefore do not intrude into the gap 11. The amount ofdeposition on sidewalls of the gap 11 was small because the sourcematerial gases do not reach there. Therefore, the susceptor 2 could beused for much more rounds of crystal growth before it needs replacement,and the productivity was enhanced accordingly.

[0052] In a lateral type apparatus in which source material gases areintroduced horizontally and flow in parallel with the substrate, thesusceptor is inclined by raising the downstream side thereof for thepurpose of uniforming the growth thickness of the film. In case ofgrowth of III-V nitride semiconductors, bridging over the boundarybetween the susceptor 2 and the support base 1 by gallium metal becomesmore serious because droplets of gallium slip down the slope. To improvethe apparatus in this respect, the second embodiment of the inventionemploys the improvement shown in FIG. 7. That is, the support base 1 hasformed grooves 12 of ridges and furrows. Thus, gallium metal drops inthe grooves 12, or downward flows of the gallium metal are interruptedby the grooves 12. Therefore, gallium metal is unlikely to accumulatebetween the susceptor 2 and the support base 1. As a result, theapparatus could be used for much more rounds of the growth process, andthe productivity thereof was enhanced.

[0053]FIG. 2 shows one of known techniques for rotating the substrate.The support base 1 and the susceptors 21 have formed annular grooves,and a plurality of carbon balls 91 are held in the grooves to supportthe susceptors rotationally. For transmission of the rotational force, agear 93 is formed at an end of each susceptor 21 and engages with anexternal stationary gear 8. When the rotary shaft 5 rotates the supportbase 1, the susceptors 21 rotate about their own axes. Although this isan excellent mechanism, it is insufficient depending upon its materials.In case the apparatus is intended for growth of GaN, for example, whichneeds a high growth temperature, the support base 1 and the susceptors21 are made of SiC or SiC-coated carbon. These are very hard materials,and the machining accuracy and the surface condition of the grooves andthe gears are worse than those made of carbon. Moreover, since sapphireballs are used instead of carbon balls 91. Therefore, the apparatus isinsufficient in lubricity, and a larger frictional force is producedduring rotation. As the rotating speed increases, large vibrations willoccur. In extreme cases, disharmony occurs among rotatable members, thesusceptors 21 will accidentally disengage eventually. Therefore, forgrowth of GaN compound semiconductors, the apparatus needs a structurereliably preventing accidental disengagement. It has been confirmed thatthis problem can be overcome by inserting an independent bearingmechanism between the support base 1 and the susceptors 2. FIG. 8 showsthe third embodiment of the invention directed to this improvement. Hereis shown only a part thereof necessary for explanation of this system.In FIG. 8, numeral 21 refers to a susceptor, and 90, 91 and 92 denotecomponents of the bearing, which are made of SiC or nitride-based newceramics. Numeral 93 denotes a gear formed on one of complementarymembers of the bearing, which is connected to the external stationarygear 8. The mechanism incorporating the bearing mechanism and preventingaccidental disengagement upon vibrations is realized by male and femalescrews 94. For assembling the mechanism, sapphire balls 91 are first putin the groove of the other complementary member 92 of the bearing fixedto the support base 1, and the other rotational member 90 is next putthereon and rotated to fasten the screws 94. Thus, the members 90 and 92engage deeper and deeper beyond the engagement of the screws 94, andbecome free as illustrated. Thereafter, the complementary members of thebearing do not disengage unless the upper member is lifted against thegravity and rotated oppositely. A gear 93 is associated with thebearing, and rotates under engagement with the external fixed gear 8.Other than the above-explained mechanism, there are various types ofmechanisms for incorporating the bearing. If a retainer is used toreduce interference between balls, more stable rotation will be ensured.

[0054]FIG. 9 shows a chemical vapor deposition apparatus according tothe fourth embodiment of the invention. Here is shown another examplerelated to the way of rotating the bearing shown in FIG. 8. In FIG. 9,numeral 95 denotes a wind pressure receiver that receives a windpressure from a gas inlet 81 and converts the energy to a rotating forcefor the bearing. This mechanism is advantageous in releasingextraordinary resistance to the bearing by slipping and being therebyfreed from destruction.

[0055]FIG. 10 shows a chemical vapor deposition apparatus according tothe fifth embodiment of the invention, which employs lamp-aided heatingfrom above as a heating means. In FIG. 10, numeral 71 denotes a lamphouse that is an integral part of the pressure container. Numeral 72denotes a halogen lamp, 73 is a cooling gas inlet path for cooling thelamp, 74 is a pressure through path opening to a downstream position ofthe reactor, and 75 is a partitioning plate for separating the gasflow-in path from the lamp portion. The partitioning plate 75 is atransparent quartz plate having a thickness of about 5 mm to about 10mm. Since the pressure through path 74 merges the exhaust gas, theexhaust gas may accidentally flow back toward the lamp upon a change inreaction pressure. To prevent it, inactive gas for the cooling purposeis continuously supplied from the cooling gas inlet path 73. Since thepressure through path 74 renders the lamp side and the substrate sideapproximately equal in air pressure, the partitioning plate 75 may bethin. This configuration makes it possible to employ the lamp-aidedheating method under a reduced pressure.

[0056]FIG. 3 shows a system for rotating a large-sized donut-shapedrotational susceptor 2 supported on the circumferential surface of thesupport base 1 and rotated when the support base 1 rotates. Thedonut-type susceptor 2 is employed in apparatuses configured to blow outsource material gases from the center in radial directions. The supportbase 1 is typically made of quartz, and the donut-type susceptor 2 isSiC-coated carbon. The support base 1 is not heated, but the susceptor 2is heated to 1100° C. for example. Therefore, these members cannot befixed, and the susceptor 2 is supported only by contact with thecircumferential surface of the support base 1. Alternatively, a guide inthe radial direction may be provided, but the susceptor 2 cannot beunited with the support base 1. Therefore, thermal expansion andcontraction in repetitive heating and cooling cause a deviation of thecenter position of the susceptor 2. To prevent the positional deviation,the sixth embodiment of the invention connects them with quartzconnection rods 100. The connection rods 100 each have fixed points onthe support base 1 and on the susceptor 2. The line connecting the fixedpoints of each connection rod 100 is offset from the diametric linepassing the fixed point on the support base 1 by a certain angle, suchas 45 degrees. In operation, when the donut-type susceptor 2 expand dueto a rise of the temperature, the inner diameter of the susceptor 2 alsoexpands. Then, in case of FIG. 3, each connection rod 100 rotates thesusceptor 2 in a direction reducing the angle from the diametricdirection, making use of the expansion force of the susceptor 2. Thus,the donut-type susceptor 2 can keep the center point upon isotropicdeformation thereof.

[0057]FIG. 4 shows a chemical vapor deposition apparatus according tothe seventh embodiment of the invention, taken as another example thatmust expand and contract while keeping the center position. In FIG. 4,numeral 21 denotes a susceptor set in a bearing mechanism. Numeral 8denotes an external stationary gear. Numeral 93 denotes cogs of the gear90 in engagement of the cogs of the external stationary gear 8. Inoperation, when the support base 1 rotates about its center point, thesusceptor 21 set on the bearing mechanism is rotated about its owncenter and together with the support base 1 by engagement of the cogs 93of the gear 90. When the temperature rises, both the support base 1 andthe external stationary gear 8 expand by thermal expansion. If theexternal stationary gear 8 expands under no restriction, i.e. under nomeans keeping the center point, the engagement becomes tight on one handand loose on the other hand. Such uniform gear engagement invitescollision of cogs and destruction thereof. The connection rods 100,however, assures smooth rotation by permitting the stationary gear 8 toexpand while keeping the center point by the same principle.

[0058] Regarding countermeasures against extraordinary rotation, almostno techniques have been taught. FIG. 11 shows a chemical vapordeposition according to the eighth embodiment of the invention, improvedin the power transmission system of the rotating system to cope withirregular operation of the apparatus. In FIG. 11, numeral 110 denotes arotary encoder, numeral 111 denotes a connector slidable or torsionallydeformable under large torque, and numeral 112 denotes a driver such asa stepping motor. Numeral 113 is a comparator of electrical signals, andnumeral 114 is an information processing device. This system operates asexplained below. Let an extraordinary torque be caused by anirregularity occur in the rotating system of the support base 1. Oncethe connector 111 slips or twists, rotation signals from the rotaryencoder 110 and rotation signals from the driver 112 disagree. Thecomparator 113 detects the disagreement, converts it to a digitalsignal, and delivers it to the information processing device 114.Responsively, the information processing device 114 analyzes theirregularity, interrupts the driver 112 and generates an alarm signal115. In this manner, destruction of the reactor can be prevented.

[0059] As the pipe arrangement for supplying source material gases tothe reactor, chemical vapor deposition apparatuses typically let carriergas flow in the main pipe, and connect source material gas pipes to themain pipe. FIG. 5 shows a conventional layout of pipes. For example, 116denotes the main pipe that is connected to the reactor at position I. InFIG. 5, the main pipe is labeled A, and source materials gas pipes arelabeled B through H. The portion of A, B is the pipe arrangement of aunit for one source material, the portion of C, D is that for two sourcematerials, and the portion of E through H is that for four sourcematerials. Typically, source material gas pipes are gathered andconnected substantially at one point as shown in FIG. 5 because, if themain pipe has a large pipe resistance, the pressure will differ amongdifferent positions of the pipe system, and will cause undesirableproblems upon switching gases. However, this arrangement of pipes hasbeen confirmed through actual use thereof to involve the problemexplained below. That is, when the flow rate of source materials gasesincreases, vibrations occurred in the flows of source materials gases.This is because that the gas pressure from one of opposed pipes, C,influences the other of the opposed pipes, D; the flow rate controller(mass flow controller, MFC) of the pipe D gives a feedback control; itsresult influences the control of the counter part pipe C; and repetitionof this cycle causes vibrations or chaotic behaviors of the gas flows.The vibrations can be controlled to a certain extent by adjusting thetime constant of the flow rate controllers. However, it has beenconfirmed that the phenomenon of vibrations can be essentially removedby using the pipe arrangement shown in FIG. 12 that illustrates theninth embodiment of the invention. That is, it is important that aplurality of pipes to be joined do not meet head-on, or their mergingpoints are distant from each other by a distance with which the changein pressure by entrance of each gas is reduced to a negligible level.From this point of view, it has been confirmed that nearest two mergingpoints of pipes should be distant at least by the interval equal to ormore than the pipe diameter.

[0060] Heretofore, some specific embodiments of the invention have beenexplained. However, the invention is not limited to these embodiments,but contemplates other various modifications based upon the technicalconcept of the present invention. For example, the first embodimentshown in FIG. 6 can be extended to a system intended for processing aplurality of substrates simultaneously. Further, although thoseembodiments have been explained as being of a face-up type, they can bemodified to a face-down type. The concept of keeping the center point bythe use of connection rods 100 is also usable for holding the bearingmechanism in the apparatus, for example. Moreover, it is applicable toall mechanisms having difficulties in fixing the center point.

[0061] As described above, according to the first aspect of theinvention in an embodiment, since the gap is provided between therotational susceptor and the support base, the apparatus is freed fromdisturbance of rotation caused by bridging of these members by deposits,and is operative for more rounds of crystal growth process. Thus, themanufacturing capability by the apparatus is enhanced.

[0062] According to the second aspect of the invention in an embodiment,grooves by ridges and furrows on the support base removes disturbance ofrotation caused by undesirable flows of deposits to the boundary withthe susceptor even in inclined reactor devices. Here again, theapparatus is operative for more rounds of crystal growth process, andenhanced in manufacturing capability.

[0063] According to the third and fourth aspects of the invention in anembodiment, the use of the independent, new bearing mechanism in therotation system ensures stable rotation of the substrate, enhances theproduction yield and improves the manufacturing capability.

[0064] According to the fifth aspect of the invention in an embodiment,the use of the pressure through path in the lamp-aided heating typeapparatus makes it possible to employ the lamp-aided heating also inpressure-reduced systems to manufacture substrates with high-qualityfilms grown thereon.

[0065] According to the sixth aspect of the invention in an embodiment,in a system including members subjected to isotropic deformation such asthermal expansion, center positions of those members can be keptconstant to ensure their stable rotational movements and enhance thecapability of the apparatus.

[0066] According to the seventh aspect of the invention in an embodimentusing a combination of the rotary encoder and the connector that canslip or twist, it is possible to stop the driver immediately upon anyirregular rotation and generate an alarm signal to prevent any damage tothe apparatus.

[0067] According to the eighth aspect of the invention in an embodimentincluding the air-aided driver directly connected to the rotary shaft,it is possible to stop the driver immediately upon any irregularrotation to prevent any damage to the apparatus.

[0068] According to the ninth aspect of the invention in an embodimentemploying the pipe arrangement for chemical vapor deposition apparatusesin which source material gas pipes do not meet head-on when they merge,high-quality crystal growth is possible without vibrations by gas flows.

[0069] It should be understood that various changes and modifications tothe presently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

1. A chemical vapor deposition apparatus characterized in that a gap isprovided along the boundary between a support base and the perimeter ofa rotational susceptor supported on the support base.
 2. The chemicalvapor deposition apparatus according to claim 1 wherein the width of thegap is equal to or wider than 0.5 mm.
 3. The chemical vapor depositionapparatus according to claim 1 wherein the width of the gap is equal toor wider than 1 mm.
 4. The chemical vapor deposition apparatus accordingto claim 1 wherein the width of the gap is controlled in the range from0.5 mm to 2 mm.
 5. The chemical vapor deposition apparatus according toclaim 1 wherein the width of the gap is controlled in the range from 1mm to 2 mm.
 6. The chemical vapor deposition apparatus according toclaim 1 wherein the depth of the gap is equal to or deeper than 1 mm. 7.The chemical vapor deposition apparatus according to claim 1 wherein thedepth of the gap is equal to or deeper than 2 mm.
 8. The chemical vapordeposition apparatus according to claim 1 wherein the depth of the gapis controlled in the range from 1 mm to 4 mm.
 9. The chemical vapordeposition apparatus according to claim 1 wherein the depth of the gapis controlled in the range from 2 mm to 3 mm.
 10. The chemical vapordeposition apparatus according to claim 1 wherein the apparatus is ametal organic chemical vapor deposition apparatus.
 11. The chemicalvapor deposition apparatus according to claim 1 wherein the apparatus isa metal organic chemical vapor deposition apparatus intended for growthof III-V nitride compound semiconductors.